The present invention relates to devices and systems for controlling the recirculation of exhaust gas (EGR) in an internal combustion engine for controlling exhaust emissions from the engine. Heretofore, such devices have employed a source of engine generated vacuum applied to pressure responsive means for operating a moveable valve for controlling flow of the exhaust gas in a recirculation passage. Typically, the control passage is connected between the engine exhaust manifold and the induction passage or intake manifold. It is also known to employ in such control devices, means for sensing exhaust gas pressure upstream of the valve member for use in modifying the effects of the vacuum as applied to the pressure responsive member for moving the control valve member.
The aforesaid EGR control devices have been generally self-contained and operate independently of other engine control devices. However, it has recently been found desireable to operate electrically actuated control devices for varying the supply of fuel to the engine and for varying control of the ignition spark in non-compression ignition engines. Where the fuel metering and/or ignition spark time are electrically controlled, it has been found desireable to employ solid state electronic controllers such as microprocessors for providing the control signals to the electric actuators which in turn vary the spark timing and fuel metering. Where such electrical engine operation control is employed, it has been found necessary to take into account the amount of exhaust gas recirculation as well as other engine parameters such as coolant temperature, RPM and engine charge mass flow. Where these latter engine parameters are monitored for the purposes of generating an electrical control signal, it will be recognized that electrical sensors or transducers are required to provide the desired sensory input to the microprocessor for operational control.
Referring to FIG. 4, a known EGR controller 12 is shown as having an exhaust gas passage inlet orifice 1, and exhaust gas passage outlet 2 with intermediate valve seat 3 and moveable valve member 4 for controlling flow between inlet and outlet. Hollows actuating rod 5 connects the valve 4 to a pressure responsive diaphragm 9 which moves in response to a vacuum signal applied to connector tube 28. Bellows 7 creates pressure chamber 6 which communicates through hollow rod 5 with the passage pressure upstream of the valve seat. Pressure transducer 8 senses pressure in bellows chamber 6, which is representative of dynamic flow pressure in the inlet passage, and the transducer 8 emits an electrical signal through leads 24, 26 which is indicative of the sensed flow pressure. The aforesaid known EGR controller has disadvantage of relying on the integrity of the resilient bellows material in withstanding the punishment of flexing while exposed to hot exhaust gas.
It has thus been desired to find improved means of providing engine EGR responsive to an electrical signal available from an on-board microprocessor employed for engine control, it has thus been desired to employ an electrical signal for control of a modulator valve for providing the vacuum control signal to the EGR controller and to provide such a device without relying on the integrity of a resilient flexing bellows exposed to hot exhaust gas.